In some applications it is desirable to apply cycling fluid flow pressures to a chamber or line. For example, alternating gas (e.g. air) pressure and draw (vacuum) may be needed in a flow line or chamber. This may be necessary, for example, if alternating expansion and contraction of an inflatable member is desired. A specific example of this is represented by the cargo transportation system which is the subject matter of applicant's copending application, Ser. No. 108,109, incorporated herein by reference.
A typical methodology that could be utilized to provide for alternating fluid flows to a single line, is through utilization of a two-way valve arrangement. For such an arrangement, the valve would be provided with a first (fluid inlet) line, a second (vacuum draw) line, and a single (third line) fluid flow outlet. The single fluid flow outlet would be in operative communication with a chamber to be subjected to the cycling fluid flows (pressure and draw). The first line, for example, could be connected to an air compressor, with the second line being in operative connection to a vacuum pump. The valve would be provided with a stopcock or other valve member selectively adjustable to allow fluid flow through the valve from the first line to the outlet, or alternatively from the outlet to the second (vacuum draw) line. Thus, the valve would have two possible fluid flow settings. Such a value is referred to herein as a two-way valve. It will be understood that if such a valve were arranged in a system having a constant pressure applied to the first line and a constant vacuum applied to the second line, alternating pressure and vacuum could be applied to the outlet line, by simply switching the valve. It is noted that cycling of pressures, or fluid types, could be provided in a similar system if instead of being associated with a vacuum draw, the second line were in communication with a fluid source different from that of the first line. Similarly, both the first and second lines could be draw lines, with the third line operating as an inlet rather than an outlet.
At least arguably, a wide variety of two-way valve arrangements, whether developed for the movement of highly viscous liquids, less viscous liquids, or gases, could be adapted for use in situations involving cycling of fluid pressure or service to a single third) line. However, for applications in arrangements such as that of U.S. Ser. No. 108,109, many conventional valves would be generally unacceptable. The reasons for this often include at least the following:
1. In some applications it is necessary, or at least desirable, that a rather large volume of fluid be passed through the valve in a very short period of time. Many conventional valve arrangements are substantially restrictive with respect to fluid flow, and thus are not readily adaptable to such uses.
2. If very rapid cycling between the two flow settings is needed, many conventional arrangements are not acceptable. For example, they may involve large, bulky, heavy and/or inefficiently designed valve members which, although they accommodate conventional applications rather well, are ineffective for rapid switching.
3. It is foreseen that at least in some applications, a very high rate of cycling for an extended period of time may be required, for operation of the system. Many conventional arrangements would not be appropriate for use in situations involving a great many cycles of the valve. For example, in some conventional arrangements, repeated movement of adjacent parts, in a relatively short time, leads to sufficient wearing of components for generation of leaks.
It will be understood that the above list is only exemplary of the types of problems encountered in adapting many conventional two-way valving arrangements, to situations wherein rapid, repeated, cycling between substantial fluid flows is needed.